1. Field of the Invention
The present invention relates to novel cationic rosin polymers useful as sizing agents for paper, to rosin salts of these polymers, to blends of these polymers with other sizing materials, to the foregoing compositions in dry particulate form and as aqueous dispersions, to paper sized by a content of the foregoing compositions, and to the several methods involved.
2. Description of the Prior Art
At the present time, rosin size is the most widely used agent for the manufacture of sized paper. Rosin size is a dispersion of rosin or one or more rosin derivatives in an aqueous medium containing sodium rosinate, and is anionic. It is generally applied by the beater addition process (i.e., it is added to the papermaking fibrous suspension before the fibers have been formed into a web), and the sizing components are deposited on the fibers by the action of alum.
Rosin size has several disadvantages as a sizing agent for paper. One disadvantage is that when it is applied by the beater addition process, as is typical, the resulting paper is acidic because the alum which is used as precipitate is acidic. As a result, paper which is produced by this process generally undergoes acid tendering, which shortens its life. A second disadvantage is that the correct proportioning of the alum and the rosin size is a significant item of technical expense. A third is that sulfate ions (from the alum) continuously build up in the white water system, requiring a portion of the white water to be bled off from the system.
The Daniel et al. U.S. Pat. No. 2,772,966 attempted to overcome these disadvantages by converting rosin to cationic form, so that it would be self-substantive to the fibers, the size being formed by transamidation of ester gum with a water-soluble polyalkylenepolyamine. The resulting size was monomeric, and perhaps for this reason a large amount of the size had to be added to provide even a moderate amount of sizing.
The use of ester gum was necessary as starting material because when rosin and a water-soluble polyalkylenepolyamine are heated together with a water-soluble polyalkylenepolyamine, the rosin forms a salt (i.e., a soap) with the polyalkylenepolyamine but does not form an amide therewith, and so the rosin is not rendered cationic.